Assessment of ballast fouling and its implications on track drainage

Australian railways offer an efficient and economic mode for transporting freight and passengers across all States. Conventionally, rail tracks are positioned on ballast for reasons including economy (availability and abundance), rapid drainage, and high load bearing capacity. However, the ballast becomes fouled due to the intrusion of fines either from the subgrade or surface which impairs track drainage. In order to maintain serviceability, it is necessary to maintain adequate drainage capacity in the track. To identify the risk associated with fouling, it is important to understand the effects of the amount of fouling on drainage conditions. In this present study a critical assessment of different types of mass based fouling indices was carried out. A new parameter, the Void Contaminant Index, which considers variations in the specific gravity of ballast and fouling materials, is proposed to evaluate the amount of fouling. A series of large scale constant head hydraulic conductivity tests were conducted to establish the relationship between the extent of fouling and the associated hydraulic conductivity. Subsequently, a seepage analysis was carried out using finite element software to simulate a more realistic two-dimensional flow under actual track geometry to capture the drainage capacity of ballast. The drainage condition of the track was classified into different categories using the average rainfall in Australia. Finally, a maintenance schedule for practising engineers was provided based on the proposed drainage criteria.